Fiber-reinforced plastics (FRP), especially carbon fiber-reinforced plastics (CFRP) are used in various fields as composite materials having light weight and high mechanical properties. As one of methods for producing molded FRP products, known is an RTM method comprising the steps of disposing a reinforcing fiber material in a molding cavity of a mold, closing the mold, injecting a flowable matrix resin into the mold, and heating for hardening or cooling for solidification. In this method, the mold is internally kept at a reduced pressure, as required.
The RTM method is one of the most suitable FRP molding methods that can effectively exhibit the light weight and high mechanical properties as the features of FRP, especially CFRP and can efficiently produce molded products having complicated shapes.
However, for removing dead portions such as strong burrs formed at the outer edge of an obtained molded product, water jet machining, NC machining or the like known is necessary as one of post-processing steps after molding. This increases the man-hours and steps of processing, to raise the cost. Especially in case of CFRP, the reinforcing fibers existing in the burrs formed at the outer edges of the molded product are too hard to allow water jet machining and so hard to necessitate frequent changes of the NC machining tool because of frequent wear. The deburring is one of the steps desired to be avoided.
To avoid the costly deburring work, various proposals are made for shaping the reinforcing fiber base material as near to a desired mold shape as possible (near net shape).
For example, it is proposed to hold a reinforcing fiber base material between upper and lower shaping molds, before disposing the reinforcing fiber base material in a mold, so that the reinforcing fiber base material can have a shape close to that of a molding shape beforehand (JP 2003-305719 A).
Further, it is proposed to apply a thermoplastic resin to a multi-layered reinforcing fiber base material and to shape the base material using a shaping mold with heating, so that the base material can have a desired shape maintained more reliably (JP 2003-080607 A).
Furthermore, it is proposed to arrange a reference line on a mold and to make a marking on a reinforcing fiber base material at a position corresponding to the reference line along a weaving yarn therein, so that the base material can be accurately positioned in the mold (JP 2003-127157 A).
However, if the above-mentioned conventional methods are used to avoid water jet machining or NC machining, etc., it is necessary to prepare a reinforcing fiber base material shaped with a size smaller than that of the intended product shape (molding precursor) before the base material is molded together with a resin, so that when the base material is disposed in a molding cavity, the base material does not protrude from the cavity, lest burrs containing reinforcing fibers should be formed.
For example, as shown in FIG. 1, in the case where a molded fiber-reinforced resin 101 used as a molded thin sheet (thickness: 0.5 to 3 mm) such as a cowl of a motorcycle is produced by the RTM method using a reinforcing fiber base material 102 shaped with a size smaller than that of the cowl shape, resin-rich portions 103 where no base material 102 exists occur at hems E1 and E2 as shown in FIG. 2. In the case where this cowl is given impact by collision, etc., there often arises such a problem that the hems E1 and E2 where the resin-rich portions 103 exist are locally broken by stress concentration.
So that the molded resin product 101 reinforced with the reinforcing fiber base material 102 has a predetermined strength also at the hems, it is necessary that the base material 102 perfectly pervades the hems E1 and E2 of the molded resin product 101. For letting the base material 102 pervade the hems of the molded resin product, a method of accurately shaping a molding precursor 100 comprising the base material 102 before disposing it into a lower mold FM was examined. However, since stitches of a woven fabric comprising reinforcing fibers used as the base material 102 were shifted, the dimensions changed greatly, and it was difficult to obtain the required dimensional accuracy (for example, about ±2 mm). Further, it is possible to accurately adjust the edge of the woven fabric disposed in the lower mold by cutting with scissors or the like, but there arose such problems that the working time became very long and that the quality depended on the skill of each worker.
Thus, it could be advantageous to provide a molding precursor that eliminates the cause of cost hike due to the water jet machining, NC machining or the like for deburring the hems E1 and E2 of the molded fiber-reinforced resin and also eliminates the cause of strength decline due to the formation of the resin-rich portions 103 devoid of the reinforcing fibers 102a. It could also be advantageous to provide a process for producing a molded fiber-reinforced resin by the RTM method using the molding precursor and a molded fiber-reinforced resin.